To solve various road traffic-related problems such as traffic accidents and traffic jams, an expressway traffic system (ITS or Intelligent Transport System) that is a new road traffic system that makes full use of the latest information technology has been developed.
To prevent road accidents from occurring from the outset, it is important to detect the behavior of the vehicle in front using an appropriate sensor so that a suitable distance can be maintained between vehicles and/or the speed of the present vehicle can be controlled. It is also important to keep the distance between vehicles constant when carrying out automatic control of a group of vehicles moving in a formation. However, if an action to be taken by the present vehicle is determined after first observing the behavior of other vehicles, there is the possibility of action being taken too slowly, and to avoid such risks, it is necessary to maintain sufficient distance between the vehicles. On the other hand, if a large distance is maintained between vehicles, it becomes difficult to monitor the behavior of other vehicles. Although it depends on the type of sensor, the sensitivity of a magnetic sensor greatly falls as the distance between vehicles increases. With an optical sensor or a sensor that uses ultrasound, in adverse weather conditions such as rain, snow, and sandstorms, obstacles are present between the vehicle and other vehicles which results in a reduction in sensitivity, with such reduction becoming larger as the distance between vehicles increases.
Instead of monitoring the behavior of other vehicles using a sensor or in addition to doing so, if it were possible to obtain in advance operation information for other vehicles, for example, information showing that the brakes have been operated to cause deceleration, that the accelerator has been operated to cause acceleration, that the steering wheel has been operated to change the course, or that the gears have been operated, it would be possible to predict the behavior of the other vehicles and therefore traveling could be made much safer. In this case, if such advance information is merely obtained, it will not be possible to make full use of the information, and it will be necessary to determine which of the vehicles moving in the periphery the advance information applies to. As the identification information of vehicles, each vehicle has a unique registration number which can be known by looking at the number plate. Japanese Laid-Open Patent Publication No. 2003-115095 discloses a technology where the driver confirms the presence of a vehicle that the driver wishes to follow using a vehicle number, control information on the lead vehicle in that vehicle group is received, and the speed of the present vehicle is controlled.
However, it is difficult to verify the number plate in a state where there is a considerable distance between vehicles. Also in adverse weather conditions, it is difficult to correctly identify a number plate with the naked eye or even with a highly sensitive sensor. In addition, when a vehicle is moving alongside the present vehicle, the number plate is physically not visible and therefore the registration number cannot be known. Even though it may be possible to specify vehicles in the periphery to an extent from the model or color, such method is not very reliable.
It is also possible to assign identification information that is suited to exchanging data by communication, such as IP addresses, and by wirelessly broadcasting operation information for the present vehicle or transmitting such information using a wireless LAN, such information can be provided to other vehicles in the periphery comparatively easily. Also, if there is a central control system that controls the traffic, such information can also be provided to other vehicles via the central control system. However, even if identification information such as IP addresses is used, it is not easy to identify other vehicles. If a radar system is installed in each vehicle, it may be possible to identify other vehicles in a range given by the definition of the radar, but it is not economical to install a radar with a definition of several meters or less. Although it may be possible to raise the resolution by using an optical system, the effectiveness of such system is questionable in adverse weather conditions. While GPS that measures radio waves from satellites to calculate the position of the present vehicle is also effective, there is not sufficient precision to clearly differentiate the positions of a plurality of vehicles that are near one another. Using a method such as electric waves that have little directivity, although it is possible to transmit the identification information of the present vehicle to nearby vehicles or a central control system that controls a plurality of vehicles, it is not possible to specify the relative positions of a plurality of vehicles.
For this reason, in the present invention, a method of precisely identifying vehicles moving side-by-side in the periphery using a simple system is provided. In addition, it is an object to provide a system that can control a vehicle even more safely using advance information from other vehicles.